The present invention relates generally to a variable engine valve control system, and in particular, to a discrete lift, variable timing engine valve control system.
In general, various throttle-less systems can be used to actively control engine valves through the use of variable lift and/or variable timing so as to achieve various improvements in engine performance, fuel economy, reduced emissions, and other like aspects. Typically, such systems are mechanical VVLT (variable valve-lift and timing), electrohydraulic VVLT, or electro/mechanical VVT (variable valve-timing). In general, mechanical VVLT systems are cam-based systems, which may have additional phasers, cams and linkage. One important limitation of such mechanical VVLT systems is that the timing and lift variations are not independent. Electro/mechanical VVT systems generally replace the cam in the mechanical VVLT system with an electro-mechanical actuator. However, such systems do not provide for variable lift.
In contrast, an electrohydraulic VVLT system is controlled by electrohydraulic valves, and can generally achieve independent timing and lift controls so as to thereby provide greater control capability and power density. However, typical electrohydraulic VVLT systems are generally rather complex, can be expensive to manufacture, and typically are not as reliable or robust as mechanical systems due to their relative complexity.
Briefly stated, in one aspect of the invention, one preferred embodiment of a valve control system for an internal combustion engine includes a housing comprising a plurality of fixed, axially spaced cylinders positioned serially one on top of the other with each of the plurality of cylinders defining a stroke respectively. The plurality of cylinders comprises a lowermost cylinder and at least one next upper cylinder, wherein the stroke of the at least one next upper cylinder is less than or equal to the stroke of a next lower cylinder. A plurality of pistons includes a lowermost piston disposed in the lowermost cylinder and at least one next upper piston disposed respectively in the at least one next upper cylinder. Each of the at least one next upper pistons engages a next lower piston during the stroke of the at least one next upper piston respectively. An engine valve is connected to the lowermost piston. A plurality of electrohydraulic valves are operable between at least an open and closed position. Each of the plurality of electrohydraulic valves is operably connected to one of the plurality of cylinders and is operable independently of the other of the plurality of electrohydraulic valves. A selected combination of the plurality of electrohydraulic valves are selectively operated between at least the open and closed positions.
In an alternative preferred embodiment of the invention, the valve control system includes a housing comprising a cylinder having a longitudinal extent and a plurality of longitudinally spaced exhaust ports communicating with the cylinder. A piston is disposed in the cylinder and is moveable therein along the longitudinal extent. An engine valve is connected to the piston. A plurality of electrohydraulic valves are operable between at least an open and closed position. Each of the plurality of valves is operably connected to one of the plurality of exhaust ports and is operable independently of the other of said plurality of electrohydraulic valves. A selected combination of the plurality of electrohydraulic valves are selectively operated between at least the open and closed positions.
In another aspect of the invention, a method for controlling an engine valve in an internal combustion engine is provided. The method includes activating a combination of the plurality of electrohydraulic valves, moving a combination of the plurality of pistons through a plurality of corresponding strokes, engaging a next lower piston with a next upper piston, disengaging the next lower piston from the next upper piston as the stroke of the next upper piston is completed and moving the engine valve in response to moving the combination of the plurality of pistons.
In yet another aspect of the invention, the method includes activating a combination of the plurality of electrohydraulic valves and opening a combination of said plurality of exhaust ports, moving the piston in a first direction, successively covering the combination of the plurality of exhaust valves with the piston as the piston moves in the first direction, and moving the engine valve in the first direction in response to moving the piston in the first direction.
The present inventions provide significant advantages over other valve control systems, and methods for controlling valve engines. For example, each of the present embodiments of the valve control system is configured as an electrohydraulic DLVT (discrete lift, variable timing) system, which achieves discrete lift and variable timing for engine valves. By employing a discrete lift control, relatively simple hydraulic valves can be used, which eliminates the need for position sensing and feedback controls in the system and thereby substantially reduces the complexity and cost of the system. In this way, a system employing discrete lift control is simpler, less expensive and more robust than an electrohydraulic VVLT system, when used in most applications. In addition, by providing a plurality of discrete lifts, the system can closely match the performance of the VVLT system under most operating conditions.